The present invention relates to semiconductor light-emitting devices such as semiconductor light-emitting diodes and semiconductor laser diodes, which are obtained using AlGaInP and AlGaAsP semiconductor materials.
One exemplary prior art semiconductor light-emitting diode (LED for short) using an AlGaInP semiconductor material is schematically illustrated in FIG. 1.
Referring now to FIG. 1, reference numeral 201 represents an n-type GaAs substrate, and 202 a clad layer comprising an n-type AlGaInP, which is formed on the substrate 201. Reference numeral 203 represents an active layer comprising AlGaInP, and 204 a clad layer comprising a p-type AlGaInP. That is, the Al concentration is preset so that the energy gap of the AlGaInP active layer 203 is narrower than those of the AlGaInP clad layers 202 and 204. A p-type AlGaAs current-spreading layer 205 is provided to expand the electric current injected from electrodes, thereby expanding the light-emitting region and so increasing the efficiency of light extraction. Reference numeral 206 stands for a contact layer, and 207 and 208 Indicate electrodes.
One exemplary prior art semiconductor laser diode (LD for short) in schematically shown in FIG. 2.
Referring here to FIG. 2, reference numeral 201 stands for an n-type GaAs substrate, and 202 a clad layer comprising an n-type AlGaInP, which is formed on the substrate 201. Reference numeral 203 represents an active layer comprising AlGaInP, and 204 a clad layer comprising a p-type AlGaInP. That is, the Al concentration is preset so that the energy gap of the AlGaInP active layer 203 is narrower than those of the AlGaInP clad layers 202 and 204; in other words, the double-hetero structure is achieved. Reference numeral 206 indicates a contact layer.
Reference numeral 205' represents a current block layer comprising GaAs, which is provided for the purpose of achieving the so-called current confinement, thereby obtaining the current density needed for laser oscillation. This layer 205' is formed by selectively etching the layer 204 to form a ridge thereon, followed by selective growth using an amorphous film such as one of SiN.sub.x.
AlGaInP or AlInP (which may hereinafter be collectively called an AlGaInP compound) have some defects; they are higher in resistivity and thermal resistance than AlGaAsP or AlGaAs (which may hereinafter be collectively called an AlGaAsP compound). Such detects lead to a problem that the operating voltage of the device becomes too high, resulting in an increase in the amount of the heat generated. This problem must be solved so as to improve the characteristics and reliability of the device, and becomes serious especially when the eight-omitting density becomes high.
The above-mentioned problem becomes by far more serious the case of a semiconductor laser where current confinement is required with an increase in the light-emitting density.
Zinc (Zn) is generally used as a dopant for a clad layer comprising a p-type AlGaInP compound, but doping should be done at high concentration so as to lower resistivity, because Zn is low in the rate of activation. In this case, however, unactivated Zn diffuses so rapidly through the AlGaInP compound crystal body that the pn junction position is often largely shifted from the light-emitting layer toward the n-type layer. This, in turn, gives rise to abnormality in the current-voltage characteristics, a drop of light output power, and an increase in the threshold current of laser. Such diffusion of Zn from the p-type AlGaInP compound layer becomes noticeable as its thickness increases. When the light-emitting layer is relatively thin as in the case of laser, the current-voltage characteristics are liable to disorder due to the diffusion of Zn. Silicon (si) having a low diffusion coefficient is effective for an n-type AlGaInP compound.
In some cases, a light-extracting layer is located next to the clad layer. The transparency of the light-extracting layer to the light-emitting wavelength is important for improving the light-extraction efficiency of LED. However, it is probable that some light-extracting layer with high transparency has high resistivity depending on composition and that the surface current spreading area in small, as a result.
With respect to the double-hetero structure, it is usually required to impart a thickness of about 1 .mu.m to about 2 .mu.m to the clad layer to ensure confinement of carriers and light in the active layer. When the AlGaInP compound is grown by a metal organic vapor phase growth technique, it is required that the feed molar ratio (V/III) between the organic metal that is the group III material and PH.sub.3 that is the group V material be very high. This incurs some inconveniences; for instance, no high growth rate can be applied, the cost of the material to be grown is much higher than the AlGaAs compound, and so on. Especially in the case of mass-production equipment of large size enabling a multiplicity of devices to be produced at the same time, problems with removal of defects become more serious.